DESPITE THEIR REPUTATION as agents of destruction, explosive volcanoes have provided a major aid to archaeologists' study of ancient human remains. Large-volume eruptions of tephra can not only quickly and thoroughly bury entire settlements and other artifacts, effectively sealing them for posterity, but also typically lay down widespread layers of ash that, when dated, serve as valuable time markers. When the date of an extensive tephra layer is known, it enables researchers to establish the relative ages of objects found within, above, or below the deposit.

I. Volcanoes as Preservers of Archaeological Sites

A. The Science of Archaeology and Its Relation to Volcanism

Almost from its inception, archaeology has been intimately associated with volcanism. In many important ways, archaeology evolved as a scientific discipline in the laboratory provided by Herculaneum and Pompeii, Roman cities located on Italy's Bay of Naples that were buried in A.D. 79 by a catastrophic eruption of Mount Vesuvius. Rediscovered in the early 18th century, the two sites were first viewed as mere repositories of artistic plunder to furnish the private estates of European collectors. By the mid-19th century, however, under the leadership of such pioneering archaeologists as Giuseppe Fiorelli, excavators at Pompeii eventually established the systematic criteria for uncovering, cataloging, and conserving antiquities that characterize archaeology today.

An interdisciplinary science that utilizes the contributions of anthropology, geology, paleontology, ethnology, chemistry, and physics, modern archaeology involves studying and interpreting the material remains of ancient human cultures. Its objectives combine scientific and humanistic goals, including the identification and analysis of artifacts to illuminate the long-forgotten cultural processes that created them. As a multidisciplinary enterprise, archaeology includes attempts to reconstruct the full spectrum of elements composing a vanished society, including such components as its economy, commerce, political organization, religious beliefs, and mythology.

Paradoxically, volcanoes, which are popularly regarded as mere destroyers, are perhaps nature's most effective preservers of ancient human structures and settlements. No other natural phenomenon can so quickly and thoroughly bury large areas, including evidence of human occupation, protecting artifacts from subsequent damage. Exposed sites gradually covered by slower geologic processes, such as sporadic flooding or sedimentation, are typically subject to severe erosion and destructive human activities, including war, vandalism, and the deliberate demolition of older edifices. By contrast, towns such as Pompeii, Herculaneum, and Akrotiri, a Bronze Age settlement on the island of Thera (Santorini), were rapidly engulfed in pyroclastic ejecta and survive relatively intact. Besides being spared the depredations inescapable in surface exposure, the buildings, artwork, and other artifacts buried by voluminous tephra falls or pyroclastic flows remain in their original context, their spacial and functional relationships largely
undisturbed. (TABLE I)

TABLE I Some Representative Archaeological Sites Related to Volcanism

Volcanism's agency in preserving the human record extends to the earliest stages of human evolution. About 3.5 million years ago, at Laetoli in Tanzania, an adult hominid and one or two smaller companions, perhaps a female and/or child, walked upright across a newly deposited layer of ash. After a brief rainstorm splattered across the area, a second ash eruption covered the hominid footprints, effectively sealing one of the oldest surviving evidence of bipedalism until its discovery by 20th century investigators.